1. Field of the Invention
The present invention relates to a method for winding an elastic yarn and to an elastic yarn winder which is capable of taking up the elastic yarn such as a polyurethane yarn alternately by two bobbin holders and transferring a continuously running elastic yarn from a full bobbin over to an empty bobbin.
2. Description of the Related Art
First, the basic constitution of an elastic yarn winder will be explained by referring to FIG. 6. The winder is provided with a lifting box 1 vertically movably mounted on a machine frame 7, and a rotatable turret 2.
In the lifting box 1 are supported a touch roller 3 and a traversing device 4. The touch roller 3 is constantly pressed against a yarn layer wound on a bobbin B located in the winding position described later, driving the bobbin B in a counterclockwise direction. The traversing device 4 is provided with a traverse guide 6, which reciprocates within a traverse range while guiding the yarn Y transversely.
The turret 2 is rotatable by a spindle not shown, on the center of a rotating shaft 14 and is driven by an induction motor 17. Two bobbin holders 15 and 16 are rotatably supported on the turret 2, each of the bobbin holders 15 and 16 holding a few bobbins B (only two bobbins are shown for simplification). The bobbin holder 15 is mounted in the winding position a and the other bobbin holder 16, in the waiting position b.
The turret 2 rotates through 180 degrees when the bobbin B in the winding position a has become full of the yarn Y, changing the positions of the bobbin holders 15 and 16; that is, the full bobbin B is placed in the waiting position b, while the empty bobbin B is set in the winding position a. At the stage that these bobbins B are set in their new positions, however, the yarn Y to be fed is still connected with the full bobbin B in the waiting position b. The empty bobbin B then catches and cuts the yarn Y, and starts winding, thus completing yarn transfer from the full bobbin B to the empty bobbin B.
A common yarn Y, such as a nylon and a polyester yarn, is led into a slit not shown which is provided in the bobbin B, where the yarn is caught and cut with a tension caused by the rotation of the empty bobbin B, on which the yarn is thus taken up.
In the case of cutting and changing an elastic yarn such as a polyurethane yarn between the bobbins B using the slit, however, a failure in yarn transfer occurs frequently. The elastic yarn extends like a rubber thread, decreasing in sectional area. Therefore, when the winding of the elastic yarn on the empty bobbin B starts after entering the slit, the elastic yarn is pulled to extend, becoming smaller in sectional form and accordingly easily movable in the slit. The yarn therefore slips in the slit, failing in transferring the yarn to the empty bobbin B.
To the elastic yarn, therefore, a method for yarn transfer as shown in FIG. 6 is adopted. The surface of the empty bobbin B is applied with plastics coating, to thereby make the elastic yarn easily attachable on the surface of the empty bobbin B. Also, the turret 2 is turned in a counterclockwise direction which is opposite to a normal direction of rotation, thus changing the relation between the empty bobbin B and the yarn Y from reverse winding to normal winding. Furthermore, for a spindle not shown, a quick-braking system is provided to stop a bobbin holder 16 for holding the full bobbin B in the waiting position.
When yarn transfer is effected from a full bobbin B to an empty bobbin B, the turret 2 is rotated in the direction illustrated. The elastic yarn Y runs while being pressed against the surface of the empty bobbin B, drawing a path to the full bobbin B off the empty bobbin B. The empty bobbin B is plastics-coated on the surface, so that the elastic yarn Y will adhere on the surface of the empty bobbin B, being snapped and wound until the empty bobbin B becomes full. In this state, the bobbin holder 16 holding the full bobbin B is quickly decelerated (the bobbin holder 15 of the empty bobbin B is normally rotating). Then, the elastic yarn between the empty bobbin B and the full bobbin B is slackened. However, the elastic yarn Y, holding on the surface of the empty bobbin B, is attracted to the empty bobbin B as indicated by a dotted line, and is cut between the empty bobbin B and the full bobbin B after making one turn around the empty bobbin B, thus being wound on the empty bobbin B. The yarn transfer is done in this manner by utilizing the property of the elastic yarn Y that the elastic yarn Y is easy to adhere to the empty bobbin B due to a great friction coefficient.
However, the above-described method of yarn transfer requires quick deceleration of the bobbin holder 16 on the full bobbin B side at the time of yarn transfer; actually only a motor for electrical braking is not enough to quickly stop the full bobbin B having a great inertia gravity, and it is necessary to provide the spindle with a large-scale mechanical braking system, which, however, has such a problem that winder construction will become complicated. There also exists such a problem that a thick elastic yarn easily becomes slackened because its adhesion increases little as compared with the inertia force acting to throw the yarn off the empty bobbin, consequently failing in yarn transfer from a full bobbin to an empty bobbin. Furthermore, in the case of little adhesion of the elastic yarn which therefore can not hold well on the bobbin surface, or in the case of an elastic yarn which is too thick to fit in the slit provided in the bobbin surface, the above-described method of yarn transfer is not suitable.